The present invention relates to a brake apparatus for braking the drive wheel of tractors and like vehicles, and more particularly to a disk brake apparatus in which a cam plate presses a brake disk against a friction surface.
Generally employed as brake apparatus for braking drive wheels of tractors and like vehicles are disk brake apparatus mounted on the side walls of the transmission case. The disk brake apparatus includes a brake disk which is mounted on the differential gear shaft of the differential unit housed in the transmission case and which is adapted to be pressed against a friction plate. More specifically stated, the apparatus further includes a movable cam plate and a stationary ball retaining plate formed with cam grooves to hold balls therebetween. The movable cam plate, when turned by a brake cam, produces a thrust in the axial direction of the differential gear shaft to thereby press the brake disk against the friction plate. With such construction in which the balls are interposed, as retained in the cam grooves, between the movable cam plate and the stationary retaining plate, the balls which are in contact with the semispherical surfaces defining the cam grooves of the retaining plate are subjected to very high sliding resistance which hinders a smooth operation. Moreover, the large amount of turning movement of the movable cam plate required makes it difficult to ensure a quick operation. Accordingly another type of construction has been proposed which includes a movable ball retaining plate and a movable cam plate, such that both the plates are made turnable in opposite directions to each other to reduce the amount of movement needed. However, since the ball retaining plate is in pressing contact with the side wall of the transmission case, the retaining plate encounters high friction resistance when turned. It is therefore still difficult to assure a quick operation.